Charles III (Spanish: Carlos III; Italian: Carlo VII; 20 January 1716 – 14 December 1788) was the King of Spain and of the Spanish Indies from 1759 to 1788. He was the eldest son of Philip V of Spain and his second wife, the Princess Elisabeth of Parma. In 1731, the fifteen year old Charles became the Duke of Parma and Piacenza, as Charles I, at the death of his childless great uncle Antonio Farnese, Duke of Parma.

In 1734, as the Duke of Parma, he conquered the kingdoms of Naples and of Sicily, and was crowned as the King of Naples and Sicily on 3 July 1735, reigning as King Charles, although he is contemporarily known as Charles VII of Naples and Charles V of Sicily. In 1738 he married the Princess Maria Amalia of Saxony, an educated, cultured woman who bore him thirteen children, eight of whom reached adulthood. Charles and Maria Amalia resided in Naples for nineteen years; she died in Madrid on 27 September 1760, at the age of thirty-five. Upon succeeding to the Spanish throne on 10 August 1759, Charles, a proponent of enlightened absolutism, on 6 October 1759 abdicated the Neapolitan and Sicilian thrones in favour of Ferdinand, his third surviving son, who became Ferdinand I of the Two Sicilies, or Ferdinand IV of Naples and Ferdinand III of Sicily. Charles III's descendants ruled the Kingdom of the Two Sicilies until 1861.

In 1713, the Treaty of Utrecht concluded the War of the Spanish Succession (1701–14), thereby reducing the political and military power of Spain, which had been ruled by the House of Bourbon since 1700. Under the terms of the treaty, the Spanish Empire retained its Latin American territories, and ceded to Habsburg Austria the Southern Netherlands, the kingdoms of Naples and Sardinia, the Duchy of Milan, and the State of Presidi. Moreover, the House of Savoy gained the Kingdom of Sicily, and Great Britain gained the island of Minorca and the fortress at Gibraltar. In 1700, Charles' father, the French-born "Philippe de France", became King of Spain. For the remainder of his reign (1700–46), Philip's parents continually attempted to regain these territories. In 1714, after the death of the king's first wife, the Princess Maria Luisa Gabriella of Savoy, the Piacenzan Cardinal Giulio Alberoni successfully arranged the marriage between Philip and the ambitious Elisabeth Farnese, niece and daughter-in-law of Francesco Farnese, Duke of Parma. Elisabeth and Philip married on 24 December 1714; she quickly proved a domineering consort, and influenced King Philip to make Cardinal Giulio Alberoni the Prime Minister of Spain in 1715.

In 1716, Elisabeth gave birth to the Infante Charles of Spain at the Real Alcázar of Madrid. He was fourth in line to the Spanish throne, after three elder half-brothers: the Infante Luis, Prince of Asturias (who ruled briefly as Louis I of Spain before dying), the Infante Felipe (who died in 1719), and Ferdinand. Because the Duke Francesco of Parma and his heir were childless, Elisabeth sought the duchies of Parma and Piacenza for Charles. She also sought for him the Grand Duchy of Tuscany, because the homosexual Gian Gastone de' Medici, Grand Duke of Tuscany was also childless. He was a distant cousin of hers, related via her great-grandmother Margherita de' Medici, giving Charles a claim to the title through that lineage. The birth of Charles encouraged the Prime Minister Alberoni to start laying out grand plans for Europe. In 1717 he ordered the Spanish invasion of Sardinia. In 1718, Alberoni also ordered the invasion of Sicily, which was also ruled by the House of Savoy. In the same year Charles' first sister, Infanta Maria Ana Victoria was born on 31 March. In reaction to the Quadruple Alliance of 1718, the Duke of Savoy then joined the Alliance and went to war with Spain. This war led to the dismissal of Alberoni by Philip in 1719. The Treaty of The Hague of 1720 included the recognition of Charles as heir to the Italian Duchies of Parma and Piacenza. Charles' half brother, the Infante Felipe Pedro, died on 29 December 1719, putting Charles third in line to the throne after Luis and Ferdinand. He would retain his position behind these two until they died and he succeeded to the Spanish throne. His second full brother, Infante Felipe of Spain, was born on 15 March 1720.

Beginning in 1721, King Philip had been negotiating with Philippe d'Orléans, the French regent, to arrange three Franco-Spanish marriages that would cement tense relations. The young Louis XV of France would marry the three year old Infanta Maria Ana Victoria and thus she would become Queen of France; Charles' half brother Luis would marry the fourth surviving daughter of the regent, Louise Élisabeth d'Orléans. Charles himself would be engaged to the pretty Philippine Élisabeth d'Orléans who was the fifth surviving daughter of Philippe d'Orléans. In 1726 Charles met Philippine Élisabeth for the first time. Out of these marriages only Luis and Louise Élisabeth would wed. There were no children from the union, Luis would be king of Spain for 8 months after his father's abdication in January 1724; Luis died in August 1724 from smallpox, and Philip retook the throne. Maria Ana Victoria was sent to Paris but never married Louis; the engagement was officially called off on 9 March 1725 and Maria Ana Victoria was sent back to Spain. In retaliation Philippine Élisabeth was returned to France in 1728. The departure of Philippine was seen as a sad affair, unlike that of her older sister Louise Élisabeth who had never been popular at the court. Philippine Élisabeth died in Paris from smallpox in 1734. Elisabeth of Parma, insulted by the French rejection of her daughter, then looked for other potential brides for her eldest son. For this she looked to Austria, its principal opponent for influence on the Italian peninsula. She proposed to Charles VI, Holy Roman Emperor that the Infante Charles marry the 8 year old Archduchess Maria Theresa and that her second surviving son, the Infante Felipe, marry the 7 year old Archduchess Maria Anna.

The alliance of Spain and Austria was signed on 30 April 1725, and included Spanish support for the Pragmatic Sanction, a document drafted by Emperor Charles in 1713 to assure support for Maria Theresa in the succession to the throne of the Habsburgs. The emperor also relinquished all claims to the Spanish throne, and promised to support Spain in its attempts to regain Gibraltar. The ensuing Anglo-Spanish War stopped the ambitions of Elisabeth of Parma, and the marriage plans were abandoned with the signing of the Treaty of Seville on 9 November 1729. Provisions of the treaty did allow the Infante Charles the right to occupy Parma, Piacenza and Tuscany by force if necessary. Two sisters and another brother were brought into the royal family between 1726 and 1729. Infanta Maria Teresa Rafaela was born in Madrid on 11 June 1726; she eventually married Louis, Dauphin of France; Infante Luis, Count of Chinchón, who Charles would later banish from the court; and the Infanta Maria Antonietta, who eventually married Victor Amadeus III of Sardinia.

After the Treaty of Seville, Philip V disregarded its provisions and formed an alliance with France and Great Britain. Antonio Farnese, the Duke of Parma, died on 26 February 1731 without naming an heir; this was because the widow of Antonio, Enrichetta d'Este was thought to have been pregnant at the time of his death. The duchess was examined by many doctors without any confirmation of pregnancy. As a result, the Second Treaty of Vienna on 22 July 1731 officially recognised the young Infante Charles as the Duke of Parma and Piacenza. The duchy was occupied by the Count Carlo Stampa, who served the lieutenant of Parma for the young Charles. Charles was from then on known as HRH Don Charles of Spain (or Borbón), Duke of Parma and Piacenza, Infante of Spain. Since he was still a minor, his maternal grandmother, Dorothea Sophie of the Palatinate, was named regent. Charles arrived in Italy on 20 October 1731. After a solemn ceremony in Madrid, Charles was given the épée d'or (Sword of Gold) by his father; the sword had been given to Philip V of Spain by his grandfather Louis XIV of France before his departure to Spain in 1700. Charles left Spain and traveled overland from Seville to Antibes; he then went to Tuscany, arriving at Livorno on 27 December 1731. His cousin Gian Gastone de' Medici, Grand Duke of Tuscany, was named his co-tutor and despite Charles being the default heir of Gian Gastone, the Grand Duke still gave him a warm welcome. En route to Florence to Pisa, Charles was taken ill with smallpox. Charles made a grand entrance to the Medici capital of Florence on 9 March 1732 with a retinue of 250 people. He stayed with his host at the ducal residence, the Palazzo Pitti.

Gian Gastone staged a fête in honour of the Patron Saint of Florence, Jean-Baptiste, on 24 June. At this fête Gian Gastone named Charles his heir, giving him the title of Hereditary Prince of Tuscany, and Charles paid homage to the Florentine senate, as was the tradition for heirs to the Tuscan throne. After the Holy Roman Emperor, Charles IV, found out about the ceremony, he was greatly enraged due to Gian Gastone not giving him Imperial nomination having the rank of ..Ruler of the Romans. Despite the celebrations, Elisabeth of Parma urged her son to go on to Parma. This he did in October 1732, where he was greeted with much joy. On the front of the ducal palace in Parma was written Parma Resurget (Let Parma rule). At the same time the play La venuta di Ascanio in Italia was created by Carlo Innocenzo Frugoni. It was later performed at the Farnese Theatre in the city.

Upon his arrival in the peninsular, Charles was not yet seventeen years old. He received the strict and structured education of a Spanish Infante; he was very pious and was often in awe of his domineering mother, who according to many contemporaries, he resembled greatly. The Alvise Giovanni Mocenigo, Doge of Venice and Ambassador of Venice to Naples declared that:

It was the same as the opinion of Count Monasterolo Solaro, ambassador of Savoy who described Charles Emmanuel III of Sardinia in 1742. On the other hand he was educated in printmaking (remaining an enthusiastic etcher), painting and a wide range of physical activities which included a future favourite of his, hunting. Sir Horatio Mann, a British diplomat in Florence noted that he was greatly impressed at the fondness Charles had for the sport. His physical appearance was dominated by the Bourbon nose that he had inherited from his father's side of the family. He was described as "a brown boy, who has a lean face with a bulging nose", and was known for his happy and exuberant character.

In 1733, at the death of Augustus II the Strong, King of Poland, there was a succession crisis in Poland. France stood opposite Austria and Russia in supporting different contenders to the throne. France joined forces with Savoy and Spain (with whom it signed the first Bourbon Compact late in 1733) to engage in the acquisition of territory at the expense of Austria. A marginal role was entrusted to the Spaniards in the north of Italy, but the principal objective of Charles' mother was for her to win the largest amount of territories for her sons. These included territories that Spain had lost in the treaty of Utrecht: the Kingdoms of Naples and Sicily. The two kingdoms had been divided by Savoy and Austria by that treaty, and Sicily had become Austrian in the 1720 Treaty of the Hague.

On 20 January 1734, his 18th birthday, Charles was given his majority and was thus able to rule as he wished, "free to govern and to manage in a manner independent its states". He was also named commander of all Spanish troops in Italy, a position he shared with José Carrillo de Albornoz, 1st Duke of Montemar. Charles, who had been given the style of Charles I of Parma, then embarked on a military campaign to take Naples and Sicily. On 27 February King Philip issued a declaration of his intention to capture the Kingdom of Naples, claiming to free it of "excessive violence [by the Austrian Viceroy of Naples], oppression and tyranny". After inspecting the Spanish troops at Perugia, Charles ordered the army to march toward Naples on 5 March. The march passed through the Papal States then ruled by Clement XII. The Austrians, who also ruled Lombardy, had only limited resources for the protection of Naples to defend against the expected Spanish invasion, and were divided on how best to defend against it. Even though the Emperor wanted to keep Naples, the majority of the Neapolitan nobility were against him, and some conspired against his viceroy. This was because they hoped that Philip would give the kingdom to Charles, who would be more likely to live and rule there, rather than having a viceroy and service a foreign power. On 9 March the Spanish took Procida and Ischia, two islands in the Bay of Naples. A week later they defeated the Austrians at sea. On 31 March (his sister Maria Ana Victoria's 16th birthday) the Bourbon troops closed in on the Austrians in Naples. The Austrian General Otto Ferdinand von Abensberg und Traun's defensive position was flanked, and he was forced to withdraw to Capua. This allowed Charles and his troops to advance onto the city of Naples itself.

The Austrian viceroy, Giulio Borromeo Visconti, and the commander of his army, Giovanni Carafa, left some garrisons holding the city's fortresses, and withdrew to Apulia. There they awaited reinforcements that they hoped would provide the resources needed to defeat the Spanish. The Spanish entered Naples and quickly gained control over the Austrian-held fortresses in the early days of April. During that interval, Charles received the compliments of the local nobility as well as the city keys and the privilege book from a delegation of the city's elected officials. Chronicles of the time reported that Naples was captured "with humanity" and that the combat was only due to a general climate of courtesy between the two armies, often under the eyes of the Neapolitans that approached with curiosity. The first fort that was taken by the Spanish army was the fortress of Carmine (10 April), with Sant'Elmo falling on 27 April, the Castel dell'Ovo on 4 May, and finally the New Castle on 6 May. This all occurred even though Charles had no military experience, seldom wore uniforms, and could only with difficulty be persuaded to witness a review.

Charles de Bourbon (Carlo di Borbone) had his triumphant entrance to Naples on 10 May 1734. He entered on a horse that entered through the old city gate at Capuana surrounded by the councillors of the city along with the a group of people who threw money at the locals. The procession went on through the streets and ended up at the Cathedral of Naples, where Charles received a blessing from the local archbishop, Cardinal Pignatelli. Charles took up residence at the Royal Palace, which had been built by his ancestor, Philip III of Spain. Two chroniclers of the era, the Florentine Bartolomeo Intieri and the Venetian Cesare Vignola both said that the Neapolitans had different views on the situation. Intieri writes that his arrival was an historic event, and that the crowd screamed that "His Royal Highness is beautiful, that his face is as the one of San Gennaro on the statue that the representative". On the contrary, Vignola wrote that "there were only some acclamations", and that the crowd applauded with "a lot of languors" and only "to incite those that threw the money to throw it in more abundance".

King Philip wrote a letter to Charles which began with the words "To the King of Naples, My Son and My Brother". Charles was unique in the fact that he was the first ruler of Naples to actually live there, after two centuries of viceroys. However, Austrian resistance had not yet been completely eliminated. The emperor had sent reinforcements to Naples directed by the Prince of Belmonte, which arrived at Bitonto. Spanish troops led by the Count of Montemar attacked the Austrians on 25 May 1734 at Bitonto, and achieved a decisive victory. Belmonte was captured after he fled to Bari, while other Austrian troops were able to escape to sea. To celebrate the victory, Naples was illuminated for three nights, and on 30 May, the Duke of Montemar, Charles' army commander, was named the Duke of Bitonto. Today there is an obelisk in the city commemorating the battle. After the fall of Reggio Calabria on 20 June, Charles also conquered the towns of L'Aquila (27 June) and Pescara (28 July). The last two Austrian fortresses were Gaeta and Capua. The Siege of Gaeta, which Charles observed, ended on 6 August. Three weeks later, the Duke of Montemar left the mainland for Sicily where they arrived in Palermo on 2 September 1734, beginning a conquest of the island's Austrian-held fortresses that ended in early 1735. Capua, the only remaining Austrian stronghold in Naples, was held by von Traun until 24 November 1734.

In the kingdom, the independence from the Austrians was popular. In July 1734, the British consul Edward Allen wrote to the Duke of Newcastle: "It is a matter certainly of a profit for this city and this kingdom that the king there lives which means that if the money between, it not some sets off again, which produced itself in an important way with the Germans that had drained all the gold of the population and almost all the money to do big gifts to the Emperor".

In 1735, pursuant to the treaty ending the war, Charles formally ceded Parma to Emperor Charles VI in exchange for his recognition as King of Naples and Sicily. In the first years of his reign, the Holy See and Charles did not have the best relationship. The Kingdom of Naples has always been closely related to the See since it had once been part of the Papal States. Pope Clement XII thought of himself as the legitimate ruler of the kingdoms and refused to recognise Charles as its ruler. For all response, a commission met in Naples and was presided over by the Tuscan lawyer, Bernardo Tanucci. It concluded that the pontifical nomination is not necessary for the coronation of a king cannot be considered as a sacrement. Tanucci, named minister of Justice, implements a political one aiming to limit harshly the strength of the clergy of which the possessions always are in increase, that benefits from the exemption of the taxes and of its own courts. The Neapolitan government does nevertheless of the gestures of relaxation as for example; it forbade the return of the historian of the Pouilles that was in exile, Pietro Giannone who was not popular with the clergy. The situation grew worse in 1735, some days before his coronation at Palermo, Pope Clement XII the Emperor to give him the annual 'Chinea which consisted of a white mare and a sum of money that was tradition for the King of Naples to give the Pope. The reason of this choice was that the Emperor was considered as the sovereign of the Kingdom of Naples, his Dyed was a custom, whereas the new king was, a novelty. This greatly angered Charles.

During this time, Charles went to Sicily even though the island's conquest had not been completed (Metz, Syracuse and Trapani were still under Austrian control). He was crowned King of Naples and Sicily on 3 July; rex utriusque Siciliae. His coronation occurred in Palermo's Cathedral; Palermo was chosen because it could bypass the authority of the pope, thanks to the apostolic legation of Sicily.

March 1735 saw a new discord enter Rome and Naples. In Rome, it was discovered that Bourbons confined Roman citizens in the Palazzo Farnese which was the personal property of the King Charles; people were brought here to impress them into the Neapolitan army. Thousands of inhabitants in the town of Trastevere stormed the palace to liberate them, which then degenerated to pillage. The crowd directed itself next toward the embassy of Spain. During the clashes that followed, several Bourbon soldiers were killed including an officer. The disturbances spread to the town of Velletri where the population attacked Spanish troops on the road to Naples. The episode was perceived as an insult to Charles and the Bourbons, and consequently the ambassadors of Spain and Naples left Rome, while apostolic nonces were dismissed from Madrid and Naples. Charles ordered that regiments of Bourbon troops were to penetrate the Papal States; the threat was so bad that some doors in Rome were under increased guard. Velletri was occupied and obliged to pay forty thousand shields as a city occupied; later on due to hostilities, Ostia was pillaged, while Palestrina avoided the same by paying a ransom of fifteen thousand shields. After the hostilities, the committee of the Cardinals decided to send a delegation of prisoners of Trastevere and of Velletri to Naples as reparations. The offenders that were caught were made to stay in prison for some time and after having asked for Royal Pardon from Charles, they were allowed to go free. Charles, thanks to the mediation of the archbishop Giuseppe Spinelli and major chaplain of the course Celestino Galiani, succeeded in overcoming their differences on 10 May 1738 after lengthy negotiations. After the death of Pope Clement in 1740, he was replaced by Pope Benedict XIV, who the following year allowed the creation of a concordat with the Kingdom of Naples. This allowed the taxation of certain property of the clergy, the reduction of the number of the ecclesiasticals and the limitation of their immunity and autonomy of the justice via the creation of a mixed tribunal.

A preliminary peace was concluded on 3 October 1735 concerning the hostilities with Austria. However, the peace was not finalized until three years later with the signing on 18 November 1738 of the Treaty of Vienna, ending the War of the Polish Succession. By the terms of the treaty, Stanisław Leszczyński renounced his claim on the Polish throne and recognized Augustus III, Duke of Saxony, as King of Poland. As compensation he received instead the Duchy of Lorraine and Bar, which was to pass to France upon his death (which occurred in 1766). Francis Stephen, who had been the Duke of Lorraine, was indemnified with the vacant throne of the Grand Duchy of Tuscany, the last Medici having died in 1737. France also agreed to the Pragmatic Sanction, guaranteeing the planned succession in Austria. The kingdoms of Naples and Sicily were ceded by Austria to Charles, who ceded Parma to Austria, and gave up his claims to the throne of Tuscany in favor of Francis Stephen. The treaty included the transfer to Naples of all the inherited goods of the House of Farnese. He took with him the collection of artworks, the archives and the ducal library, the cannons of the fort and even the stairway of marble of the ducal palace. As a result of the peace, Charles' mother Elisabeth again began looking for potential brides for her son, now formally recognised as King of Naples and Sicily throughout Europe. Impossible to get an Archduchess of Austria as a bride, she looked to Poland, choosing Princess Maria Amalia of Saxony, a daughter of Augustus III and his (ironically) Austrian wife Maria Josepha of Austria. Maria Josepha was a niece of the Emperor; the marriage was seen as the only alternative to the Austrian proposal.

Maria Amalia was only 13 when she was informed of her proposed marriage and that the Pope had given his permission and blessing on the marriage. The marriage date was confirmed on 31 October 1737. Maria Amalia held a proxy wedding ceremony at Dresden in May 1738 with her brother, Frederick Christian of Saxony representing Charles. This marriage was looked upon favourably by the Holy See and effectively meant the conclusion of the diplomatic disagreement Charles and the See had had. The couple met for the first time on 19 June 1738 at Portella, a village on the frontier of the kingdom near Fondi. At court, festivities lasted till 3 July when Charles created the Insigne e reale ordine di San Gennaro — the most prestigious order of chivalry in the kingdom. He later had the Order of Charles III created in Spain on 19 September 1771.

The peace between Charles and Austria was signed in Vienna in 1740. That year, Emperor Charles died leaving his Kingdoms of Bohemia and Hungary (along with many other lands) to his daughter Maria Theresa; he had hoped the many signatories to the Pragmatic Succession would not interfere with this succession. However, this was not the case, and the War of the Austrian Succession broke out. France was allied with Spain and Prussia, all of whom were against Maria Theresa. Maria Theresa was supported by Great Britain, ruled by George II, and the Kingdom of Sardinia, which was then ruled by Charles Emmanuel III of Sardinia. Charles had wanted to stay neutral during the conflict but his father wanted him to join in and gather troops to aid the Spanish. Charles arranged to send to Spain 10,000 men under the control of Duke of Castropignano, but they were obliged to retreat when British forces threatened to bombard the port of Naples if they did not stay out of the conflict. The decision to remain neutral was again revived and was poorly received by the French and his father in Spain. Charles' parents encouraged him to take arms as his brother Infante Felipe had done. After publishing a proclamation on 25 March 1744 reassuring its subjects, Charles took the command of an army against the Austrian armies of the prince of Lobkowitz, who were at that point marching for the Neapolitan border.

In order to oppose the small but powerful pro-Austrian party in Naples, a new council was formed under the direction of Tanucci that resulted in the arrest of more than 800 people. In April Maria Theresa addressed the Neapolitans with a proclamation in which she promised pardons and other benefits for those who rose against the "usurpers", meaning the Bourbons. The participation of Naples and Sicily in the conflict resulted, on 11 August in the decisive Battle of Velletri, where Neapolitan troops directed by Charles and the Duke of Castropignano, and Spanish troops under the Count of Pledges, defeated the Austrians of Lobkowitz, who retreated with heavy losses. The courage shown by Charles caused the King of Sardinia, his enemy, to write that "it revealed a worthy consistency of his blood and that it behaved glorious". The victory at Velletri assured Charles the right of being able to give the title Duke of Parma' to his younger brother Infante Felipe. This was recognised in the Treaty of Aix-la-Chapelle signed in 1748; it was not till next year that Infante Felipe would officially be the Duke of Parma, Piacenza and Guastalla.

In 1746, Philip V of Spain died in Madrid aged 62. The throne of Spain was inherited by Infante Ferdinand who was crowned Ferdinand VI of Spain. Ferdinand, who hated his step mother, made her leave the Spanish court; this also meant that Elisabeth of Parma would not have as much influence over her son on the pretext that she was the queen of the realm. The same year saw the introduction of the Inquisition to Charles' domains bought by the Cardinal Spinelli; this was not popular at all and it required the intervention of Charles.

Charles left a lasting legacy on his kingdom; he built much and introduced reforms in the country. In and around Naples can be found a collection of palaces that he constructed during his reign. In awe of the Palace of Versailles and the Royal Palace of Madrid in Spain (the latter being modeled on Versailles itself), Charles undertook and oversaw the construction of one of Europe's most lavish palaces, the Palace of Caserta (Reggia di Caserta). Construction ideas for the stunning palace started in 1751 when he was 25 years old. The site had previously been home to a small hunting lodge, as had Versailles, which he was fond of because it reminded him of San Ildefonso where the Royal Palace of La Granja de San Ildefonso was located in Spain. Caserta was also much influenced by his wife, the very cultured Maria Amalia of Saxony. The site of the palace was also far away from the large volcano of Mount Vesuvius which was a constant threat on the capital as was the sea. Charles himself that laid its foundation stone amid much festivity on his 26th birthday, 20 January 1752.

Other buildings he had built in his kingdom were the Palace of Portici (Reggia di Portici), the Teatro di San Carlo — constructed in just 270 days — and the Palace of Capodimonte (Reggia di Capodimonte); he also had the Royal Palace of Naples renovated. He and his wife had the Capodimonte porcelain Factory constructed in the city. He also founded the Ercolanesi Academy and the Naples National Archaeological Museum, which still operates today.

In Naples Charles began making internal reforms which he afterwards continued in Spain. The chief minister in Naples, Bernardo Tanucci, had a considerable influence over him. It was during his rule that the Roman cities of Herculaneum (1738), Stabiae and Pompeii (1748) were re-discovered. The king encouraged their excavation and continued to be informed about findings even after moving to Spain. Charles also encouraged the development of skilled craftsmen in Naples and Sicily, after centuries of foreign domination. Charles is recognized for having recreated the "Neapolitan nation", building an independent and sovereign kingdom. He is also the craftsman of a deep politics of reformations - administrative,  social and  religious - that the kingdom awaited for a long time. Charles was the most popular king the Neapolitans had had for many years. He was very supportive of the people's needs, regardless of class, and has been hailed as an Enlightenment king. Among the initiatives aimed at bringing the kingdom out of difficult economical conditions, Charles created the "commerce council" that negotiated with the Ottomans, Swedes, French and Dutch. He also founded an insurance company and took measures to protect the forests, and tried to start the extraction and exploitation of the natural resources.

The Kingdom of Naples remained neutral during the Seven Years' War (1756 – 1763). The British Prime Minister, William Pitt wanted to create an Italian league where Naples and Sardinia would fight together against Austria, but Charles refused to participate. This choice was sharply criticised by the Neapolitan Ambassador in Turin, Domenico Caraccioli. With the Republic of Genoa relations were stretched: Pasquale Paoli, general of Corsican pro-independence rebels, was an officer of the Neapolitan army and the Genoese suspected that he received assistance of the kingdom of Naples.

After Charles departed for Spain, Minister Tanucci presided over the Council of Regency that ruled until Ferdinand reached 16, the age of majority. At the end of 1758, Charles' half brother Ferdinand VI was displaying the same symptoms of depression that their father used to suffer from. Ferdinand lost his devoted wife, Infanta Barbara of Portugal in August 1758 and fell into deep mourning for her. He named Charles his heir on 10 December 1758 before leaving Madrid to stay at Villaviciosa de Odón, where he died on 10 August 1759. At that point Charles was proclaimed King of Spain under the name of Charles III of Spain, respecting the third Treaty of Vienna, which stated he would not be able to join the Neapolitan and Sicilian territories to the Spanish throne. He was later given the title of Lord of the Two Sicilies. The Treaty of Aix-la-Chapelle, that Charles had not ratified, foresaw the eventuality of his accession to Spain; thus Naples and Sicily went to his brother Philip, Duke of Parma, while the possessions of the latter were divided between Maria Theresa (Parma and Guastalla) and the King of Sardinia (Plaisance). Determined to maintain the hold of his descendants on the court of Naples, Charles undertook lengthy diplomatic negotiations with Maria Theresa, and in 1758 the two signed the Fourth Treaty of Versailles, by which Austria formally renounced the Italian Duchies. Charles Emmanuel III of Sardinia, however, continued to pressure on the possible gain of Plaisance and even threatened to occupy it. In order to defend the Duchy of Parma from Charles Emmanuel's threats, Charles deployed troops on the borders of the Papal States. Thanks to the mediation of Louis XV, Charles Emmanuel renounced his claims to Plaisance in exchange for financial compensation. Charles thus assured the succession of one of his sons and, at the same time, reduced Charles Emmanuel's ambitions. According to Domenico Caracciolo, this was "a fatal blow to the hopes and designs of the king of Sardinia".

The eldest son of Charles, Infante Felipe, Duke of Calabria, was mentally retarded and was thus taken out of the line of succession to any throne; he died quietly and forgotten in Portici where he had been born in 1747. The title of Prince of Asturias was given to the heir to the Spanish throne who was in effect the Prince born, Carlos of Naples and Sicily. The right of succession to Naples and Sicily was reserved for his second son Prince Ferdinand of Naples and Sicily; Prince Ferdinand would stay in Italy while his father was in Spain. Charles' formally abdicated the crowns of Naples and Sicily on 6 October 1759, in favor Ferdinand. Prince Ferdinand became King of Naples and Sicily, at only eight years old, under the name of Ferdinand IV of Naples and as Ferdinand III of Sicily; in order to consolidate the alliance with Austria for he was destined to marry Maria Carolina of Austria. Charles left his son's education and care to a Regency Counsel which was composed of eight members. This counsel would govern the kingdom until the young king was 16 years old. Ferdinand and Maria Carolina eventually married and had 18 children.

Charles and his consort arrived in Barcelona on 7 October 1759. Unlike his twenty years in the Italian Peninsula which had been very fruitful, the era on mainland Spain is often regarded with less joy. Internal politics, as well as diplomatic relationships with other countries underwent complete reform. Charles represented a new type of ruler: the ruler who followed Enlightened absolutism. This was a form of absolute monarchy or despotism in which rulers embraced the principles of the Enlightenment, especially its emphasis upon rationality, and applied them to their territories. They tended to allow religious toleration, freedom of speech and the press, and the right to hold private property. Most fostered the arts, sciences, and education. Charles shared these ideals with other monarchs, including Maria Theresa of Austria, her son Joseph, and Catherine II of Russia. The principles of the Enlightenment were applied to his rule in Naples and he intended to do the same in Spain though on a much larger scale. Charles went about his reform along with the help of the Marquis of Esquilache, Count of Aranda, Count of Campomanes, Count of Floridablanca, Ricardo Wall and the Genoan aristocrat Jerónimo Grimaldi.

The first tragic event that Charles had to deal with was the death of his beloved wife Maria Amalia. She died at the Palace of Buen Retiro on the eastern outskirsts of Madrid. She was aged 35 and died on 27 September 1760 of tuberculosis. She was buried at the El Escorial in the royal crypt. The traditional friendship with France brought about the idea that the power of Great Britain would decrease and that that of Spain and France would do the opposite; this alliance was marked by a Family Compact signed on 15 August 1761 (called the "Treaty of Paris"). Charles had become deeply concerned that Britain's success in the Seven Years War would destroy the balance of power, and they would soon seek to conquer the Spanish Empire as they had done the French.

In early 1762, Spain entered the war. The major Spanish objectives to invade Portugal and capture Jamaica were both failures. Britain not only repulsed the Spanish attack on Portugal, but captured the cities of Havana and Manila. Charles III wanted to fight on the following year, but he was persuaded by the French leadership to cease combat. The 1763 Treaty of Paris saw Spain cede Florida to Great Britain in exchange for the return of Havana and Manila. This was partly compensated by the acquisition of a portion of Louisiana given by France as a compensation for Spain's war losses.

In the Falklands Crisis of 1770 the Spanish came close to war with Great Britain after expelling the British garrison of the Falkland Islands. However Spain was forced to back down when the British Royal Navy was mobilised and France declined to support Spain.

The rivalry with Britain also led him to support the American revolutionaries in their War of Independence despite his misgivings about the example it would set for the Spanish Colonies. During the war, Spain recovered Minorca and British West Florida in military campaigns, but failed to regain Gibraltar. Spanish military operations in West Florida and on the Mississippi River helped the Thirteen Colonies secure their southern and western frontiers from British attack. The capture of Nassau in The Bahamas enabled Spain to also recover East Florida during peace negotiations. The Treaty of Paris of 1783 confirmed the recovery of Florida and Minorca, and restricted the actions of British commercial interests in Central America.

His internal government was, on the whole, beneficial to the country. He began by compelling the people of Madrid to give up emptying their slops out of the windows, and when they objected he said they were like children who cried when their faces were washed. At the time of his accession to Spain, Charles named Marquis of Esquillache secretary to the Finances and Treasurer and both realised many reforms. The Spanish Army and Navy were reorganised despite the losses from the Seven Years War. Charles also eliminated the tax on flour and generally liberalised most commerce. Despite this action, it provoked the overlord to charge high prices because of the "monopolizers"' speculating on the bad harvests of the previous years. On 23 March 1766, his attempt to force the madrileños to adopt French dress for public security reasons was the excuse for a riot (Motín de Esquilache) during which he did not display much personal courage. For a long time after, he remained at Aranjuez, leaving the government in the hands of his minister Count of Aranda. Not all his reforms were of this formal kind.

Campomanes tried to show Charles that the true leaders of the revolt against Esquilache were the Jesuits. The wealth and power of the Jesuits was very large; and by the royal decree of 27 February 1767, known as the Pragmatic Penalty of 1767, the Jesuits were expelled from Spain, and all their possessions were confiscated. His quarrel with the Jesuits, and his memory of the Pope while he was King of Naples turned him towards a general policy of restriction of what he saw as the overgrown power of the Church. The number of reputedly idle clergy, and more particularly of the monastic orders, was reduced, and the Spanish Inquisition, though not abolished, was rendered torpid. In spite of his hostility to the Jesuits, his dislike of friars in general, and his jealousy of the Spanish Inquisition, he was a very sincere Roman Catholic.

In the meantime, much antiquated legislation which tended to restrict trade and industry was abolished; roads, canals and drainage works were established. Many of his paternal ventures led to little more than waste of money, or the creation of hotbeds of jobbery; yet on the whole the country prospered. The result was largely due to the king, who even when he was ill-advised did at least work steadily at his task of government. In Spain he continued with his work trying to improve the services and facilities of his people. He created the Luxury Porcelain factory under the name of Real Fábrica del Buen Retiro in 1760; Crystal followed at the Real Fábrica de Cristales de La Granja and then there was the Real Fábrica de Platería Martínez in 1778. During his reign, the areas of Asturias and Catalonia industrialised quickly and produced much revenue for the Spanish economy. He then turned to the foreign economy looking towards his colonies in the Americas. In particular he looked at the finances of the Philippines and encouraged commerce with the United States, starting in 1778. He also carried out a number of public works; he had the Imperial Canal of Aragon constructed, as well a number of routes which led to the capital of Madrid, which is located in the centre of Spain. Other cities were improved during his reign; Seville for example saw the introduction of many new structures such as hospitals and the Archivo General de Indias. In Madrid he was nicknamed the Better Mayor of Madrid, "el rey alcalde". Charles was responsible for granting the title "Royal University" to the University of Santo Tomás in Manila, which is the oldest in Asia.

Charles was the godfather of the daughter of Marie Antoinette, Marie-Thérèse Charlotte de France. Marie-Thérèse was born and baptised on 19 December 1778; the uncle of the princess the comte de Provence stood in proxy for Charles.

In the capital he also had the famous Puerta de Alcalá constructed along with the statue of Alcachofa, and moved and redesigned the Real Jardín Botánico de Madrid. He had the present National Art Museum of Queen Sofia (named in honour of the present Queen of Spain, born Princess Sophia of Greece and Denmark) built, as well as the renowned Museo del Prado. At Aranjuez he added wings to the palace. He created the Spanish Lottery and introduced Christmas cribs following Neapolitan models. During his reign, the movement to found "Economic Societies" (an early form of Chamber of Commerce) was born.

The example of his actions and works was not without effect on other Spanish nobles. In his domestic life, King Charles was regular, and was a considerate master, though he had a somewhat caustic tongue and took a rather cynical view of humanity. He was passionately fond of hunting. During his later years he had some trouble with his eldest son and daughter-in-law. If Charles had lived to see the beginning of the French Revolution he would probably have been frightened into reaction.

He died on 14 December 1788 at the Royal Palace of Madrid; the palace had undergone much alteration under his rule; it was in his reign that the huge Comedor de gala (Gala Dining room) was built during the years of 1765 – 1770; the room took the place of the old apartments of Queen Maria Amalia. He was buried at the Pantheon of the Kings located at the Royal Monastery of El Escorial.

It was under Charles' reign that Spain began to be recognised a nation rather than a collection of kingdoms and territories. His efforts resulted in the creation of a National Anthem, a flag, and a capital city worthy of the name, and the construction of a network of coherent roads converging on Madrid. On 3 September 1770 Charles III declared that the Marcha Real was to be used in official ceremonies. It was also Charles who chose the colours of the present flag of Spain; red and yellow. The flag of the military navy was introduced by the king on 28 May 1785. Until that date, Spanish vessels had sported the white flag of the Bourbons with the arms of the sovereign. This was replaced by Charles due to his concern that is looked too similar to the flags of other nations.

The arms that Charles sported while King of Spain were used till 1931 when his great great great grandson Alphonso XIII lost the crown, and the Second Spanish Republic was proclaimed (there was also a brief interruption from 1873-5). Juan Carlos I of Spain, Spain's current ruler, is a direct male line descendant of the "rey alcalde". Juan Carlos is a descendant of Charles by four of his great grandparents, and is also a descendent of Maria Theresa of Austria.